Specs:

In the HK USP Expert, the following goes extremely well:

Edit: 5.3Gn was too low for the USP so upped to 5.5Gn

Trial loads made to be tested:

Reliable load with 140gn ALSAPRO and Bold BA9 seems to be 5.0gn.

The OAL was derived by dropping the loaded cart into the barrel. The OAL of 1.15“ was touching the rifling with the ogive of the LOS 123gn bullets, so needed to shorten the OAL to avoid out-of-battery. The crimp was taken from the Wikipedia article stating the CIP dimensions of the case and should be considered a starting point.

The starting load was derived from a forum post of someone stating Vihtavuori Oy had emailed them, saying 3.0gn of N310 is a safe starting point, and the experience of fellow shooters using 3.4gn in their CZ's and Glocks. Main goal is as low recoil as possible, retaining enough cycle energy.

Secondary source: the Reloading Made Easy- forums

3.4gn start and 3.9gn MAX, 1.122" min COL (28.5mm)

Powder is 50e/7700gn so 0.006493506E/gn making 3.8gn to be 0.247E